The effect of precipitation on microwave LMDS networks-performanceanalysis using a physical raincell model

This article proposes an application of the EXCELL model to microwave local multipoint distribution systems. With EXCELL, validated in many years of observations with a meteorological radar, rain is modeled by a population of exponentially-profiled raincells. Their statistics can be made to honor any given rainfall cumulative distribution function. It is, thus, possible to simulate synthetic precipitation events so that rain effects on various radio link topologies (point-to-point or multipoint) can be evaluated on each event. Both copolar and crosspolar effects were modeled, and the C/I and C/N statistics were evaluated for a large number of events     

Radio-frequency and microwave dielectric properties of insects.

Basic principles and definitions of dielectric properties of materials are presented. Data from the literature on the dielectric properties of insects are briefly reviewed and discussed in relation to insect control by selective dielectric heating. Because early measurements of the dielectric properties of insects were taken on bulk samples of insects (insect and air-space dielectric mixtures), a means for converting the dielectric properties, or permittivities, of bulk samples of particulate materials to those of the solid particles is described. The technique uses the Landau & Lifshitz, Looyenga dielectric mixture equation and information on the bulk densities of air-insect mixtures used for dielectric properties measurements along with the densities of the insects. Such converted data for the dielectric constants and loss factors of the insects are presented and collected for comparison with other measurements of insect tissues and permittivity determinations from more recent microwave measurements of these same parameters. Resulting data are presented for reference, and comparisons are presented and discussed briefly.     

The physical properties of CdTe doped with V and Ge

CdTe:(V, Ge) single crystals are grown using the Bridgman-Stockbarger method. The impurity concentrations in the melt are N_V = 1 × 10¹⁹ cm^?3 and N_Ge = 5 × 10¹⁸ and 1 × 10¹⁹ cm^?3. Electrical and galvanomagnetic characteristics are studied in the temperature range 300–400 K. It is found that the equilibrium characteristics are governed by deep levels (ΔE = 0.75–0.95 eV) located close to the midgap. Low-temperature optical absorption spectra indicate that the impurity levels of V and Ge ions in the low-energy region are in different charge states. In addition, the samples are annealed in Cd vapor and then rapidly cooled. This annealing causes the decomposition of various complexes formed during the crystal growth and an increase in both electrical conductivity and charge carrier concentration.     

Nanotwin formation and its physical properties and effect on reliability of copper interconnects

Ultra-fine grained copper with a large amount of nano-scale twin boundaries has high mechanical strength and maintains normal electrical conductivity. The combination of these properties may lead to promising applications in future Si microelectronic technology, especially as interconnect material for air-gap and free-standing copper technologies. Based on first principles calculations of total energy and in-situ stress measurements, high stress followed by stress relaxation during the Cu film deposition seems to have contributed to nanotwin formation. Nanoindentation studies have shown a larger hardness for copper with a higher nanotwin density. The effect of Cu nanotwin boundaries on grain growth was investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The presence of a high density of nanotwin boundaries may improve the reliability of Cu interconnects.     

The effect of volume humidity and the phase composition of water on the dielectric properties of wood at microwave frequencies

The influence of volume humidity on the dielectric properties of wood is studied experimentally. Common features and differences in the behavior of dielectric characteristics of different wood species (birch, poplar, spruce, and larch) are revealed. It is established that the water accumulated in wood falls in no less than three categories according to its dielectric properties. The humidity dependences of the dielectric properties of wood are found to change as a result of thermal treatment. A refraction model is applied to describe the dielectric characteristics of wet wood.     

Influence of the magnetoelastic effect on the microwave magnetic properties of Fe-N thin films

The microwave permeability of nitrogen-doped iron films deposited on a flexible lavsan substrate has been experimentally investigated. The measurements were performed with the use of a coaxial transmission line. The coaxial samples were coiled from a flexible film in two different ways: with the deposited layer facing outward and with the deposited layer facing inward. It has been found that the measured frequency dependences of the permeability of the two samples strongly differ. A comparison is made between the microwave permeabilities measured in the coaxial transmission line and in a strip transmission line, in which planar samples were used. It is shown that investigation of the influence of the magnetoelastic effect on the magnetic properties at microwave frequencies can provide additional information on the magnetic structure of the material.     

Small-signal characterization of microwave and millimeter-waveHEMT's based on a physical model

A highly efficient generalized physics-based approach for small-signal characterization of FET devices is presented. A novel method is developed for extracting the frequency dependent two-port parameters from a single time-domain physical simulation based on a multi-signal excitation scheme. The technique is applied to simulating the frequency- and bias-dependent scattering parameters of HEMT's using a quasi-two-dimensional physical model that incorporates the main physical phenomena which govern the device behavior. A new carrier energy distribution model is presented which improves the accuracy of the physical model. An equivalent circuit is also generated from the physical dynamic simulation which can be used for predicting S-parameters and for indirect linking of the physical model to existing CAD tools. The unique formulation and efficiency of the present technique make it suitable for computer aided design of FET subsystems. The accuracy and flexibility of this approach is demonstrated by comparison of simulated results with measured data for a pulse doped pHEMT and uniformly doped GaAs channel HEMT     

The effect of solution concentration on the physical and electrochemical properties of vanadium oxide films deposited by spray pyrolysis

Vanadium oxide thin films were prepared on glass substrates by using the spray pyrolysis technique.The effect of solution concentration(0.1 M,0.2 M and 0.3 M) on the nanostructural,electrical,optical,and electrochromic properties of deposited films were investigated using X-ray diffraction,scanning electron microscopy,UV–vis spectroscopy,and cyclic volta-metrics.The X-ray diffraction shows that only the sample at 0.1 M has a single β-V2O5phase and the others have mixed phases of vanadium oxide.The lowest sheet resistance was obtained for the samples prepared at 0.3 M solution.It was also found that the optical transparency of the samples changes from 70% to 35% and the optical band gap of the samples was in the range of 2.20 to 2.41 eV,depending on the morality of solution.The cycle voltammogram shows that the sample prepared at 0.3 M has one-step electerochoromic but the other samples have two-step electerochoromic.The results show a correlation between the cycle voltammogram and the physical properties of the films.     

Study of microwave damage effect on HEMT low noise amplifier under different drain voltage bias

The microwave damage effect on high electron mobility transistor (HEMT) low noise amplifier (LNA) under different drain voltage bias is studied using TCAD simulation and experiments. Simulation and experimental results suggest that the damage power thresholds and damage locations of single stage LNA under different drain voltage bias are almost the same. Nevertheless, the output power under zero drain bias is about 5.6 dB higher than it under normal (3 V) drain bias with the injection of large power microwave pulses. In Addition, the output power relative to it under normal drain bias decreases linearly with the increase of drain bias, following the function of P_dB = − 1.85V_ds + 5.7. For multi-stage LNA, the observation using optical microscope reveals that the first and second stage HEMT of LNA under zero drain bias are both damaged while only first stage HEMT of LNA under normal bias is damaged with the injection of same large power microwave pulses, which is consistent with simulated output characteristics results.     

Analysis of the effect of sodium on the physical properties of an oxide-coated cathode

A method for computer simulation of atomic sodium adsorption, desorption, and diffusion in an oxide-coated cathode is proposed. The problems are solved with TURBO PASCAL codes. The results of the in situ experiment are compared with the results of the computer simulation. The comparison confirms the vacancy mechanism of the diffusion.     

The effect of atmospheric stability on microwave excess emissivitydue to wind

The excess microwave emissivity of the ocean surface due to winds at nadir incidence is derived from the TOPEX microwave radiometer and altimeter together with ocean surface data. The sensitivity of emissivity to wind speed is found to depend strongly on the air-sea temperature difference     

Computer studies of the effect of electron and hole current multiplication factors on the d.c. and microwave properties of symmetrical Si DDR IMPATT devices

Computer studies are presented on the effect of carrier current multiplication on the d.c. field and current profiles and the small-signal admittance of a symmetrical Si double-drift region (DDR) IMPATT diode, taking into account the realistic field dependence of ionization rate and drift velocity of charge carriers and also the effect of mobile space-charge. The d.c. field and current profiles indicate that the lowering of the electron current multiplication (M_n) is more effective than the lowering of hole current Multiplication factor (M_p) in modifying the d.c. properties of Si DDR devices. The computer-aided small-signal analysis carried out for the same structure shows that, a lowering of M_n leads to a sharp decrease of the peak value of the small-signal negative conductance at a fixed d.c. current density which is accompanied by a shift of the frequency range of oscillation towards the higher frequency side.     

The influence of substrate properties on microwave losses in thin films of semiconductors

A method is presented for the contactless measurement at microwave frequencies of the resistivity of thin films of semiconductors deposited on insulating substrates. The resistivity is determined through a measurement of the change in the power loss or Q of a microwave cavity upon insertion of the sample. In addition to the intended application, knowledge can be obtained about microwave power losses in supported thin films. Calculated microwave losses in the semiconductor films are presented in a normalized form as a function of the thickness and electrical properties of both the film and the supporting substrate at 9.0 GHz (X band) and 23.0 GHz (K band). These calculations were made for germanium on calcium fluoride and sapphire substrates. The power losses are normalized on a unit surface area and a unit surface field intensity basis. Limited experimental data are presented for germanium on calcium fluoride. The computed curves show that a maximum in power dissipation for a fixed substrate thickness and frequency is reached at higher and higher film resistivities as the film thickness increases. A very strong dependence of power loss on substrate thickness is demonstrated.     

Equivalent actions of high-power microwave and video pulses with different polarities on semiconductor diode structures

The energy, power, and temperature characteristics of semiconductor p-n junction structure and the structure with a Schottky barrier are simulated under the actions of a high-power microwave and video pulses with different polarities. The results of simulations are presented. The temperature fields are comparatively analyzed using the numerical model of drift-diffusion thermal approximation and the interval estimates of the energy equivalence under the actions of pulses of different types.     

The microstructure and physical properties of thin SnO2 films

Thin polycrystalline SnO₂ films were deposited on glass substrates by magnetron sputtering. Electrical, optical, and gas-sensing properties, as well as the structure and phase composition of the films, were studied. The electrical resistance of the films and the concentration and mobility of free charge carriers were determined by the four-point-probe and van der Pauw methods. The band gap and the type of optical transitions in the films were derived from optical absorption spectra. The sensitivity to toxic and explosive gases was measured. The composition, morphology, and crystal structure of the films annealed at 600°C were examined by X-ray diffraction and electron microscopy. The films were found to contain only a tetragonal SnO₂ phase and have good crystallinity. The average grain size in the annealed films is 11–19 nm. A model of the electrical conduction in the polycrystalline SnO₂ films is discussed.     

The effect of ionizing radiation on the characteristics of silicon-germanium microwave integrated circuits

The effect of ionizing radiation on the characteristics of silicon-germanium microwave ICs has been experimentally studied. Radiation tolerance criteria have been established and absolute tolerance levels of the SiGe ICs to dose and pulse ionizing radiation have been determined. Comparative analysis of the tolerance factors of the microwave ICs fabricated using different technologies is made.     

The effect of emitter doping gradient on fTin microwave bipolar transistors

The effect of the emitter doping gradient on the transit time in microwave bipolar transistor structures has been investigated. The range of gradients was chosen to cover those typically found in shallow phosphorus- and arsenic-emitter diffusions. The results show that there is appreciable free carrier storage in the emitter space charge layer. The Storage decreases when the doping gradient in the junction is increased. This effect can account for the improved fTvalues of arsenic emitter transistors. The free carrier storage in the emitter space charge layer is compared with predictions deduced from the theoretical analysis of Morgan and Smits [1].     

The variability of the ionospheric total electron content and its effect on satellite microwave communications

Rotation of linearly polarized waves (Faraday rotation) passing through the ionosphere causes depolarization in frequency reuse satellite communication systems. As the ionospheric total electron content (TEC) is not constant, dynamic compensation for this effect may be required. This paper investigates the magnitude of the TEC variations, the time scales of the variability and the predictability of the excursions. Analysis of long-term TEC measurements shows that the variations are statistical with yearly and seasonal trends strongly coupled to long term solar and geophysical effects. Short-term variations are difficult to predict. Data indicate that reliable Faraday rotation estimates can be made for 99·9 per cent of the time, provided that long-term solar, seasonal and geographical factors are considered. Occasional bursts of solar activity limit the accuracy of long-term predictions.     

The measurement of rainfall in Papua New Guinea,and its effect on microwave propagation

A programme of measurement on rainfall characteristics has been commenced at Lae, Papua New Guinea, using pluviometers, tipping bucket rain-gauges and a rapid-response rain-gauge. Pluviographs extending over many years have been analysed by computer to give data on general rain conditions and on the probability of rainfall intensity exceeding particular levels. The resultant distribution compares well with the empirical formula of Moupfouma, and corresponding parameters are given. Simultaneous measurements are also being made on the 12 GHz signal level variation from the Aussat television signal, and on the attenuation on a 10 GHz terrestrial link.